An optoelectronic component is specified.
One object to be achieved consists in specifying an optoelectronic component wherein heat generated during operation is dissipated particularly efficiently.
In accordance with at least one embodiment of the optoelectronic component, the optoelectronic component comprises a connection carrier, on which a radiation-emitting semiconductor chip is arranged.
The connection carrier is a circuit board, for example, on which or in which are arranged electrical conductor tracks and connection locations which serve for making electrical contact with the radiation-emitting semiconductor chip. The connection carrier is then embodied as substantially planar in the manner of a plate. That is to say that in this case the connection carrier has no cavity in which a radiation-emitting semiconductor chip is arranged.
Furthermore, it is possible for the connection carrier to have at least one cavity for receiving a radiation-emitting semiconductor chip. In this case, the connection carrier can comprise a reflector that reflects electromagnetic radiation generated by the radiation-emitting semiconductor chip during operation. In this case, the connection carrier can be formed, for example, from a carrier strip (also called: leadframe) that is encapsulated by molding with an electrically insulating material such as a plastic or a ceramic material.
The radiation-emitting semiconductor chip is preferably a luminescence diode chip, that is to say a light-emitting diode chip or a laser diode chip. The radiation-emitting semiconductor chip can be suitable for generating electromagnetic radiation in the UV, infrared or visible spectral range.
In accordance with at least one embodiment, the optoelectronic component comprises a conversion element. The conversion element is a component part of the optoelectronic component which contains a luminescence conversion substance or is formed from a luminescence conversion substance.
If, for example, electromagnetic radiation generated by the radiation-emitting semiconductor chip during operation impinges on the conversion element, then the electromagnetic radiation can be completely or partly absorbed by the luminescence conversion substance in the conversion element. The luminescence conversion substance then re-emits electromagnetic radiation comprising other, preferably higher, wavelengths than the electromagnetic radiation emitted by the radiation-emitting semiconductor chip during operation. By way of example, during passage through the conversion element, part of the electromagnetic radiation from the blue spectral range generated by the radiation-emitting semiconductor chip is converted into electromagnetic radiation from the yellow spectral range.
In accordance with at least one embodiment of the optoelectronic component, the conversion element surrounds the semiconductor chip in such a way that the semiconductor chip is surrounded by the conversion element and the connection carrier. That is to say that the conversion element is stretched above the semiconductor chip for example in the manner of a dome.
In other words, the semiconductor chip is then arranged between connection carrier and conversion element. The conversion element forms, for example, a cavity above the semiconductor chip. The semiconductor chip is fixed by its mounting surface onto the connection carrier, for example. At its side surfaces and at its radiation exit surface facing away from the mounting surface the semiconductor chip is surrounded by the conversion element spanning the semiconductor chip. In this case, the conversion element preferably does not directly adjoin the semiconductor chip, rather further materials are arranged between semiconductor chip and conversion element.
In accordance with at least one embodiment of the optoelectronic component, the conversion element consists of one of the following materials: ceramic, glass ceramic. That is to say that the conversion element is not formed by a luminescence conversion substance introduced in silicone or epoxy resin as matrix material, rather the conversion element is formed with a ceramic material or a glass ceramic material.
The conversion element is preferably embodied such that it is mechanically self-supporting. The conversion element can be embodied for example as a self-supporting dome or shell that spans the semiconductor chip. Suitable ceramics for forming such a conversion element are explained in greater detail in the document WO 2007/148253, the disclosure content of which is hereby expressly incorporated by reference. Suitable glass ceramic materials are described for example in the document US 2007/0281851, the disclosure content of which is hereby expressly incorporated by reference. In the present case, a glass ceramic material is preferably not a matrix material composed of glass into which a ceramic material—for example in the form of particles—is introduced. Rather, a combination of sintered-together crystallites and a melt is involved. In particular, the term “glass ceramic” denotes materials which are produced from glass melts by controlled crystallization. The processing of the melt proceeds analogously to the processing in the case of glasses, but the glass is finally converted into a partly crystalline and partly vitreous, ceramic state by means of a special thermal treatment. The result is a glass-like product having new properties.
In accordance with at least one embodiment of the optoelectronic component, the conversion element is fixed to the connection carrier. That is to say that the conversion element has a mechanical, fixed connection to the connection carrier. By way of example, the conversion element can be connected to the connection carrier by means of a thin adhesive layer. Furthermore, it is possible for the conversion element for example to be bonded to the connection carrier or to be connected to the connection carrier by means of a press fit.
In accordance with at least one embodiment of the optoelectronic component, the optoelectronic component comprises a connection carrier on which a radiation-emitting semiconductor chip is arranged, a conversion element fixed to the connection carrier, wherein the conversion element spans the semiconductor chip in such a way that the semiconductor chip is surrounded by the conversion element and the connection carrier, and the conversion element consists of one of the following materials: ceramic, glass ceramic.
In this case, the optoelectronic component described here makes use, inter alia, of the following insight: a glass ceramic material or a luminescent ceramic for the conversion element is generally distinguished by a thermal conductivity that is significantly higher than, for example, the thermal conductivity of silicone. Preferably, the glass ceramic material or the luminescent ceramic has a thermal conductivity of ≧1.0 W/mK.
A conversion element formed from one of said materials is therefore distinguished by a particularly high thermal conductivity. On account of the fixing of the conversion element to the connection carrier, the conversion element is furthermore thermally conductively connected to the connection carrier and thus, for example, to a heat sink on which the connection carrier can be applied. Heat generated during the conversion of radiation passing through in the conversion element can be dissipated particularly well in this way.
By way of example, the conversion element consists of a YAG:Ce ceramic. Such a conversion element is distinguished by a thermal conductivity of approximately 14 W/mK.
Furthermore, a conversion element composed of the materials mentioned forms a mechanically stable protection of the semiconductor chip spanned by the conversion element against external mechanical effects. Therefore, alongside an improved heat balance, the component described is also distinguished by an improved mechanical stability.
In accordance with at least one embodiment of the optoelectronic component, at least one intermediate region is arranged between the semiconductor chip and the conversion element, said at least one intermediate region being filled with a gas. That is to say that the space between semiconductor chip and conversion element can be filled with a gas at least in places. By way of example, said gas can be air. An intermediate region filled with a gas between semiconductor chip and conversion element can further improve the dissipation of heat from the conversion element to the connection carrier on which the semiconductor chip is applied.
In accordance with at least one embodiment, the semiconductor chip is embedded in a shaped body. That is to say that the semiconductor chip is enveloped by the shaped body in a form locking manner at least in places at its uncovered outer surfaces and can be in direct contact with the semiconductor chip at these places.
In this case, the shaped body can be embodied as a potting, for example. The shaped body is as far as possible completely transmissive to the electromagnetic radiation generated by the radiation-emitting semiconductor chip during operation. That is to say that the shaped body consists of a material which absorbs hardly any or no radiation of the radiation-emitting semiconductor chip at all.
By way of example, the shaped body is formed from a silicone, an epoxide, or from a silicone-epoxide hybrid material. The shaped body encloses the semiconductor chip in a form locking manner at the free outer surfaces thereof and can have a spherically curved outer surface, for example.
Preferably, the shaped body is, in particular, free of a radiation-absorbing material such as, for example, a luminescence conversion material. That is to say that the shaped body comprises no luminescence conversion substance apart from extremely small impurities.
In accordance with at least one embodiment of the optoelectronic component, an intermediate region filled with a gas extends between the shaped body and the conversion element. By way of example, the intermediate region is filled with air.
The intermediate region preferably directly adjoins the shaped body. That is to say that the shaped body has an outer surface which faces away from the semiconductor chip and at which said shaped body adjoins the intermediate region. In this case, the intermediate region can extend as far as the connection carrier.
In this case, the intermediate region can be embodied in a dome-like manner. At its inner surface facing the shaped body, it follows the form of the outer surface of the shaped body. At its outer surface facing the conversion element, it can follow the course of the inner surface of the conversion element.
In this case, the intermediate region makes use of the following insight, inter alia: during the operation of the optoelectronic component, as a result of the heating of the radiation-emitting semiconductor chip, the shaped body in which the semiconductor chip is embedded is also subjected to heating. This heating, particularly if the shaped body contains a silicone, can lead to the thermal expansion of the shaped body. The intermediate region is dimensioned, then, in such a way that the shaped body does not come into contact with the conversion element despite said thermal expansion. That is to say that the conversion element and the shaped body, preferably, including during the operation of the optoelectronic component, are always separated from one another by the intermediate region, such that shaped body and conversion element are not in direct contact with one another. This prevents, inter alia, a situation in which, on account of the expanding silicone in the case of a temperature increase, a lift-off of the conversion element arises on account of the pressure of the shaped body on the conversion element.
In accordance with at least one embodiment of the optoelectronic component, the optoelectronic component comprises a coupling-out lens, which adjoins the outer surface of the conversion element, said outer surface facing away from the semiconductor chip. The coupling-out surface can be in direct contact with the outer surface of the conversion element. In this case, the coupling-out lens can constitute a separately produced element of the optoelectronic component which, for example, is milled, turned or injection-molded and fixed above the conversion element in a mounting step.
Furthermore, it is also possible, however for the coupling-out lens to be produced on the further component parts of the optoelectronic component and to be applied for example directly as a potting onto the conversion element.
The coupling-out lens is at least substantially transmissive to the electromagnetic radiation emitted by the optoelectronic component and/or by the conversion element. In particular, the coupling-out lens is preferably free of a luminescence conversion substance. That is to say that the coupling-out lens comprises no luminescence conversion substance apart from extremely small impurities.
In accordance with at least one embodiment of the optoelectronic component, the coupling-out lens has an inner surface, which faces the semiconductor chip and which is enclosed by an inner hemispherical surface having the radius Rconversion. Furthermore, the coupling-out lens has an outer surface, which faces away from the semiconductor chip and which is encloses an outer hemispherical surface having the radius Router. In this case, the two radii, have the following condition: Router≧Rconversion×nlens/nair. In this case, nlens and nair are the refractive indices of the coupling-out lens and, respectively, of the surroundings of the coupling-out lens, typically of air.
The inner and outer hemispherical surfaces can be purely virtual surfaces that are not necessarily embodied or do not necessarily occur as substantive features in the component. In particular, the coupling-out lens meets the above-mentioned condition, also known as “Weierstrass” condition, if the hemispherical shell formed by inner and outer hemispherical surfaces having said radii lies in its entirety within the coupling-out lens.
In particular, it is also possible for the coupling-out lens to be embodied as a spherical shell whose inner radius is given by Rconversion and whose outer radius is given by Router. In this case, in a manner governed by production, the form of the coupling-out lens can deviate slightly from the mathematically exact spherical form for inner and outer surfaces.
In other words: if the coupling-out lens meets the abovementioned condition, then the coupling-out lens is shaped and spaced apart from the semiconductor chip in such a way that the outer surface of the coupling-out lens, as seen from every point of the semiconductor chip, appears at such a small angle that no total reflection occurs at the outer side of the coupling-out lens. A coupling-out lens that obeys this condition therefore has only very low radiation losses on account of total reflection at its outer surface. The coupling-out efficiency of the optoelectronic component is thus advantageously increased.
In accordance with at least one embodiment of the optoelectronic component, the shaped body in which the optoelectronic semiconductor chip is embedded is enclosed by a hemispherical surface having the radius Rinner. In this case, the semiconductor chip has a radiation exit surface having the area content A.
In this case, the area content A and the radius Rinner meet the condition A≦½×Π×Rinner2. Preferably, the area content A is in this case ≧ 1/20×Π×Rinner2. In this case, it is assumed that a single shaped body envelops the radiation-emitting semiconductor chip of the optoelectronic component. Such a small area content of the radiation exit surface of the radiation-emitting semiconductor chip ensures that, for example, electromagnetic radiation reflected back or emitted from the conversion element to the semiconductor chip impinges with low probability on the semiconductor chip, where it might be lost by absorption, for example.
By way of example, in this case, a reflective layer is arranged on that side of the connection carrier which faces the shaped body, said reflective layer directly adjoining the shaped body at least in places and having a reflectivity of at least 80% both for electromagnetic radiation generated by the semiconductor chip and for electromagnetic radiation generated by the conversion element, preferably of at least 90%. Particularly preferably, the reflective layer has a reflectivity of at least 98%. In this case, the reflective layer is preferably situated within the hemisphere having the radius Rinner. In this way, radiation impinges with high probability on the reflective layer and not on the radiation exit surface of the radiation-emitting semiconductor chip.
In accordance with at least one embodiment of the optoelectronic component, at least one conversion substance is applied to the conversion element, said at least one conversion substance at least partly absorbing electromagnetic radiation generated by the semiconductor chip during operation and/or electromagnetic radiation re-emitted by the conversion element. The conversion substance applied to the conversion element is preferably a conversion substance which is different from the conversion substance from which or with which the conversion element is formed. That is to say that the conversion element and applied conversion substance absorb and/or re-emit electromagnetic radiation having different wavelengths or in different wavelength ranges.
By way of example, the conversion substance can be applied to the inner surface of the conversion element, said inner surface facing the semiconductor chip. That is to say that electromagnetic radiation emitted by the semiconductor chip during operation firstly impinges on the conversion substance arranged at the inner surface of the conversion element. Said conversion substance partly or completely converts the radiation into electromagnetic radiation having a different wavelength. This electromagnetic radiation then passes into the conversion element, which said radiation passes through, without being converted, or in which said radiation is in turn partly or completely converted.
By way of example, the semiconductor chip generates electromagnetic radiation in the UV spectral range during operation. The conversion substance can then be provided for converting said UV radiation at least partly, preferably as far as possible completely, into electromagnetic radiation in a different, for example in the blue, spectral range. The conversion element is then designed to convert part of this converted, blue electromagnetic radiation into electromagnetic radiation in the yellow spectral range, for example. In this way it is possible, by means of a semiconductor chip that generates electromagnetic radiation in the UV range, to realize a component that emits white mixed light.
In this case, applying the additional conversion substance on the conversion element proves to be particularly advantageous with regard to thermal properties of the component as well. This is because heat generated in the conversion substance is emitted to the conversion element, which dissipates the heat to the connection carrier on account of its high thermal conductivity. Preferably, an interspace filled with gas, for example with air, is situated between the semiconductor chip and the shaped body possibly surrounding it, on the one hand, and the conversion substance, on the other hand.
In accordance with at least one embodiment of the optoelectronic component, an adhesive is arranged between the conversion element and the connection carrier, said adhesive directly adjoining the conversion element and the connection carrier. In this case, the adhesive is preferably applied in a thin layer having a thickness of at most 10 μm, preferably at most 6 μm. Such a thin adhesive layer ensures that heat generated by the conversion element can be emitted to the connection carrier particularly efficiently.
In accordance with at least one embodiment of the optoelectronic component, the conversion element and/or the conversion substance contain(s) a luminescence conversion substance or consist(s) of a luminescence conversion substance which is based on one of the following materials: orthosilicate, thiogallates, sulfide, nitride, fluoride.
In accordance with at least one embodiment of the optoelectronic component described here, the conversion element and/or the conversion substance are/is formed with a luminescence conversion substances which is activated by at least one of the following dopants: Eu3+, Mn2+, Mn4+.
In this case, the optoelectronic component described here is based on the following insight, inter alia: as a result of the relatively large distance between semiconductor chip and conversion element and/or conversion substance in the optoelectronic component described here, the electromagnetic radiation generated by the semiconductor chip during operation is distributed over a relatively large area and over a relatively large volume. The use of slowly decaying phosphors is possible as a result. In this case, slowly decaying phosphors are understood to be phosphors which have a decay time of >1 μs. These include luminescence conversion materials activated with Eu3+, Mn2+, Mn4+, for example. As a result of the relatively large distance between the semiconductor chip, conversion element and/or conversion substance, a saturation effect becomes unlikely even in the case of said slowly decaying phosphors. For faster phosphors such as YAG:Ce, for example, which have a shorter decay time, saturation effects are even completely avoided in the case of the present optoelectronic component.
Furthermore, on account of the distribution of the electromagnetic radiation over a larger area and over a larger volume, it is possible to use luminescence conversion materials having an increased sensitivity to radiation damage, for example as a result of UV radiation. Nitrides such as e.g. Sr2Si5N8:Eu and also sulfides, oxynitrides and fluids can be mentioned here by way of example. These luminescence conversion materials can actually be used expediently for the first time in the optoelectronic component as described here.
On account of the fact that the conversion element in accordance with at least one embodiment of the optoelectronic component consists of a ceramic or a glass ceramic, the effective surface area of the phosphor is extremely reduced on account of the sintering of the luminescence conversion substances. As a result, however, slow chemical reactions with moisture, CO2, oxygen or other atmospheric gases are largely prevented since a reduced reaction surface area is available. This concerns, in particular, luminescence conversion substances such as sulfides, orthosilicates or nitrides. On account of the use of a conversion element consisting of ceramic or a glass ceramic, the lifetime of the conversion element and thus of the entire optoelectronic component is thus also increased.
On account of the fact that slowly decaying luminescence conversion materials such as narrowband f-f line emitters (for example Eu3+, Mn4+) can now be used for the first time in conjunction with semiconductor chips that emit UV radiation, it is possible to achieve high color rendering values and efficiency values of the optoelectronic component. The disadvantage of early onset saturation effects does not occur in this case.
Furthermore, in the component described here, it is possible to use luminescence conversion substances having low activator concentrations, with a concentration of up to 1/100 of what is customary in conventional luminescence conversion substances. That is to say that the component described here also enables the use of luminescence conversion substances which otherwise cannot be used on account of their poor thermal behavior, their sensitivity to atmospheric gases or their slow decay time. These include, for example, blue-green to red-orange emitting orthosilicates, thiogallates, Sulfides, nitride, fluoride and/or narrowband f-f line emitters.